Cardiac conduction system 12 lead system rules for normal ECG. Determination of heart rate

1. Interpretation of
Electrocardiogram
(ECG)
Dr.Nidhi Ahya(Asst Prof)
Cardio-Vascular & Respiratory PT
DVVPF College of Physiotherapy,
Ahmednagar 414111

2. Objectives
• Cardiac conduction system
• 12 lead system
• rules for normal ECG.
• Determination of heart rate.

11. Lead Systems- 12
lead ECG
Bipolar Limb Leads -3
Precordial Chest Leads-6
Augmented Leads-3

13. Anatomic Groups

14. Determine regularity
Look at the R-R distances
Regular -are they equidistant apart?
Occasionally irregular?
Regularly irregular?
Irregularly irregular?
R R

15. The 10 rules for a
normal ECG

16. Rule 1
PR
interval
Millivolts
Milliseconds
0 200 400 600
-0.5
0
0.5
1.0
P
R
T
Q
S
PR interval should be 120
to 200 milliseconds (0.12-
0.2 sec) or 3 to 5 little
squares

17. Rule 2
Millivolts
Milliseconds
0 200 400 600
-0.5
0
0.5
1.0
QRS
P
R
T
Q
S
The width of the QRS
complex should not
exceed 110 ms, less than
3 little squares

18. Rule 3
I II III aVR aVL aVF
The QRS complex should
be dominantly upright in
leads I and II

19. Rule 4
I II III aVR aVL aVF
QRS and T waves tend to
have the same general
direction in the limb leads

20. Rule 5
P
Q
T
S
All waves are negative in lead aVR

21. Rule 6
V1
V2
V3
V4
V5
V6
The R wave in the precordial leads must grow from
V1 to at least V4

22. I II III aVR aVL aVF V1 V2 V3 V4 V5 V6
Rule 7
The ST segment should start isoelectric
except in V1 and V2 where it may be elevated

23. Rule 8
I II III aVR aVL aVF V1 V2 V3 V4 V5 V6
The P waves should be upright in I, II, and V2 to V6

24. Rule 9
I II III aVR aVL aVF V1 V2 V3 V4 V5 V6
There should be no Q wave or only a
small q less than 0.04 seconds in width in
I, II, V2 to V6

25. Rule 10
I II III aVR aVL aVF V1 V2 V3 V4 V5 V6
The T wave must be upright in I, II, V2 to V6

26. Determination of Heart
Rate

27. Grid Methods – Regular
rhythms
1500/No.of small squares between 2
consecutive R
300/No.of large squares between 2
consecutive R

28. Scan Method - irregular
Check for 3 sec/ 6 sec markers
Count the number of QRS complexes
between markers
Multiply by 20 / 10 for 3 & 6 sec markers
respectively

30. Decreased Automaticity
Sinus
Bradycardia

31. Increased/Abnormal Automaticity
Sinus
tachycardia

32. Normal Sinus Rhythm
ECG Characteristics: Regular narrow-complex rhythm
Rate 60-100 bpm
Each QRS complex is proceeded by a P wave
P wave is upright in lead II & downgoing in lead aVR

33. Sinus Bradycardia
HR< 60 bpm;
Every QRS narrow, preceded by p wave
Normal in well-conditioned athletes
HR can be<30 bpm in children, young adults during sleep, with up to 2 sec
pauses

34. Sinus tachycardia
HR > 100 bpm, regular
Often difficult to distinguish P and T waves

35. Sinus Arrhythmia
Variations in the cycle lengths between P waves/ QRS complexes
Will often look irregular on exam
Normal P waves, PR interval, normal, narrow QRS

36. Atrial Fibrillation
Caused by a large reentrant circuit in the wall of the right atrium
Caused by numerous wavelets of depolarization spreading throughout the
atria simultaneously, leading to an absence of coordinated atrial contraction.

37. Ventricular tachycardia
Ventricular tachycardia is usually caused by reentry, and most commonly
seen in patients following myocardial infarction

38. Ventricular fibrillation

39. Summary
• What is cardiac conductive system.
• 12 leads of ECG.
• Rules for normal ECG
• Determination of heart rate.

40. QUESTIONS
1. WHAT ARE THE RULES OF NORMAL
ECG? 5MARKS
2. DESCRIBE THE 12 LEADS OF ECG.
5MARKS

41. Thank you